Where to start with "endgame"

I think you're overstating the importance of haste. Yes, haste is good, but what a new player needs is accuracy, especially if they're interested in delve NMs.

If they need accuracy bad enough to sacrifice important stats like haste they should be eating sushi.

It's different a well organized linkshell, but in pick up groups which never have proper support, I'm seeing DDs with madrigals and sushi still parse below 60% accuracy even before the NMs go into rage mode. Sushi helps, but it isn't auto-cap accuracy even for well geared players on some of these NMs.

Yes, pick better geared players etc., but this is really the only way for new players to get into delve, which was the premise of the discussion.